THE RIPENING OF CREAM. rE 
accuracy the species of bacteria present in cream when the 
total number mounts up into the hundreds of millions per 
cubic centimeter is very great. It can of course be accom- 
plished only by the study of the colonies upon the gelatin 
plates and differentiating these as well as possible. After long 
experimenting we found it possible to do this to a certain 
extent. When the plates are made with milk sugar-litmus 
gelatin there are four types of acid colonies produced. One 
of these is that characteristic of the common B&B. acid lactict 
(No. 206 of our list described in a previous report*), easily 
recognized from its being intensely acid, robust, growing under 
the surface of the gelatin, but not on the surface, and showing 
on its edge minute radiating projections. A second (No. 202 
of our previous list), is an extremely minute colony, also grow- 
ing under the surface of gelatin, commonly transparent and 
smooth and intensely acid. The third (No. 208 of our list), 
is B. lactis aerogenes, and is characterized by an extremely in- 
tense acidity, a very robust, large colony with a dense surface 
growth, and frequently producing gas bubbles. These three 
are readily distinguishable. A fourth acid type we have been 
obliged to refer to as miscellaneous acids, for it consists of all 
colonies showing acid reaction but not having the type of one 
of the three mentioned. In our experiments, the colonies of 
this fourth class have been few in unripened cream, and almost 
never present in the ripened cream. ‘Their numbers are so 
small that they have been omitted in the following tables. 
The acid bacteria of ripened cream, in other words, consist of 
a mixture of the three organisms referred to, Nos. 206, 202 
and 208. So large a proportion of the bacteria present in 
ripened cream do these three organisms form that all others. 
must be regarded as incidental. 
While these three species have thus shown themselves very 
abundant and easy to differentiate, we are by no means con- 
vinced that this classification represents three distinct species. 
Indeed, we have abundant evidence that each represents a type 
rather than a species. As is explained in a previous publi- 
cation,+ there are numerous varieties of the B. aczdz lactict, 
varying in several points, especially in the amount of acid 

* Report of Storrs Station, 1899. 
+ Idem. 
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